do not use any fix with ammonium in it. I use plain hypo crystals from bostick and sullivan. I thinkk its 150 grams in one liter or a 100 grams. I can not remmeber. my notes are in my darkroom. After applying silver nitrate I wait 45 minutes to one hour for exposure. after exposure 5-10 minutes in a 1-3% koscher salt solution, then wash 10 minutes in water, tone, then fix. I have had some problems with fixer taking too much off before, but that was because i would make it fresh, then use it immediately, with in minutes (not letting it cool down first). so now, before I use/apply silver nitrate, I mix a fresh batch of fix for the session. While i apply silver nitrate and let paper dry, the hypo can cool down. Best of luck I do not know for sure whats up???